1. Field of the Invention
The present invention relates to a method for forming casting molds and more particularly to a method for forming casting molds for casting hollow metal castings, and further relates to a flexible pattern to be used therefor.
2. Description of the Prior Art
With the progress of casting techniques in recent years there have been published several techniques recently developed relating to methods for forming casting molds, for instance, a method for forming a foamed polystyrene-series vanishing type casting mold, in which the foamed polystyrene is to be destroyed by combustion. A further method for forming a casting mold includes coating a pattern with a thin plastic film at its surface, filling a flask with casting sand and coating the back surface of the flask with a plastic film, and also coated with a plastic film at its back surface, and then reducing the atmospheric pressures in the pattern as well as in the flask by means of a vacuum pump. The method of forming a foamed polystyrene series vanishing type mold has the advantage, as compared with conventional mold-forming methods, of not requiring such operations as the withdrawal of a pattern, but is attended with disadvantages that there is produced a large amount of gas due to the combustion of polystyrene when molten metal is poured into the casting mold, and that the method itself is expensive, because the mold must be newly prepared for each casting. Therefore, countermeasures are required to avoid these disadvantages. The method of forming a casting mold, in which the pressures in the pattern and in the flask are reduced by means of a vacuum pump, has many advantages as compared with conventional casting molds, in that a bond is applied, but it is not free from the disadvantages that, when casting hollow metal castings, such operations as partitioning and reassembling the flask and the board are required, the precision of the measurements is required and further that high precision of measurements is required and that the problem of saving labour remains unsolved.